When transformed with a recombinant vector carrying the ubiC gene (encoding chorismate pyruvate-lyase, EC 4.1.3.27) the triple mutant (Phe(-), Trp(-), Tyr(-)) Klebsiella pneumoniae 62-1 excretes 4-hydroxybenzoic acid instead of chorismic acid, The recombinant strain can be used to produce in high yield specifically ring-labelled 4-hydroxybenzoic acid from isotopically labelled glucose.